WorkflowExecution: Change tags to jsonb

What does this PR do and why?

Describe in detail what your merge request does and why.

Change tags attribute in WorkflowExecution to jsonb which matches GA4GH WES spec. Set default tags in WorklowExecutions::CreateService and remove tags from being settable by the user when submitting a workflow execution.

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Run the server
Run db migrations
Navigate to a Project of your choice
Select samples and submit a pipeline
In rails console verify that tags are set.
```
WorkflowExecution.last.tags
```
Should look something like
```
=> {"createdBy"=>"admin@email.com"}
```

PR acceptance checklist

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[x] I have evaluated the PR acceptance checklist for this PR.

phac-nml / irida-next